The present invention relates generally to warning devices.
It has heretofore been generally known to provide a variety of emergency alarm devices for swimming pools and other restricted bodies of water, in which a float-supported tilt switch is operable to set off an electrically activated alarm device such as a buzzer, bell, siren or other type of audible alarm.
The known devices range from very simple float alarms to more complex and sophisticated alarm arrangements which differ primarily as to their alarm control circuitry.
U.S. Pat. No. 3,276,007 is exemplary of the known simple alarm arrangements, and discloses a float-carried alarm device which is directly connected with a battery energizing circuit containing a mercury switch that is adapted to open and close the energizing circuit in response to tilting movements of the float due to agitation of the water surface by an entering object or person. While such simple alarms were economical to produce, their operation was intermittent and spasmodic due to the opening and closing of the sensor switch rather than producing a continuous alarm once the switch closed and energizing circuit.
Later known developments are exemplified by U.S. Pat. No. 3,732,556 which discloses an alarm control circuit that overcomes the problem of intermittent operation as just described for the simple type of circuit and employs means for locking in the alarm circuit once the alarm has been activated, and in this manner produces a loud and continuous alarm which is less likely to go undetected. For such purpose, the control circuit of this patent utilizes the sensing switch means in the gate circuit of an SCR (silicon controlled rectifier) which operates to activate an energizing circuit of the alarm device, and once having operated locks in until a reset switch is activated.
The present invention proposes to provide a pool alarm having an improved electronic control circuit in which the sensor switch is utilized to control a transistor trigger circuit connected with the SCR gate to obtain (1) greater stability, (2) increased protection for the sensitive gate of the SCR, and (3) means whereby the sensitivity of the alarm unit may be adjustably controlled.